Ionic discharge tube



Aug. 12, 1941. M. J. DRUYVESTEYN 3 IONIC DISCHARGE TUBE Filed Nov. 7,1959 I Jinan/7'01? M JDrzgue's-Zeyz Patented Aug. 12, 1941 Iomc mscnaaoaTUBE Marl Johan Druyvesteyn, Eindhoven, Netherlands, assignor, by meaneassignments, to Hartford National Bank and Trust Company, Hartford,Conn., as trustee Application November 7, 1939, Serial No. 303,297

' 3 Claims.

This invention relates to an ionic discharge tube having a separatesupply of mercury communicating with the discharge space proper via aseparating member. This supply serves in well-known manner for makingupfor losses of the vapour filling in the tube and by its temperature tomaintain a given vapour pressure therein.

Particularly with discharge tubes for very high anode voltages themaintenance of constant conditions in the discharge vessel when in useis of substantial importance. The risk that consequential disturbancesmay occur which may lead, for example, to back ignitions in thenon-conducting phase is very great particularly when the tube has beencut out of circuit for comparatively long time so that its various partshave assumed the surrounding temperature and is then connected intocircuit again so that the aggregate is heated again and assumes theoperating temperature within a certain time of retardation, for examplefrom minutes to one hour and more.

In the above described heating process an excessive quantity of mercuryvapour received from the liquid mercury at a temporarily warmer spot maybe deposited on a temporarily colder spot, e. g. on a thermally moreinert electrode and cause back ignition. This is due to the fact thatthe electrodes generally have a. higher thermal capacity than thecorresponding part of the wall of the vessel and a rapid equalization ofthe temperatures of the electrodes and the wall of the vessel isprevented by the resistance to the flow of heat from these electrodes tothe medium which serves to cool the tube. Thus, during th heating-up ofthe tube the risk of harmful mercury deposit is particularly high.

It is already known to. arrange a supply of mercury in a separate vesselwhich is preferably provided at the coldest spot of the tube and whichis in communication with the discharge space proper in such manner thatflowing about of the supply of mercury in the latter is avoided and asfar as possible only the mercury vapour can pass into the dischargespace. Particularly two forms of construction were proposed for thispurpose, one of which has a constriction, for example in the form ofacapillary tube, whereas with the other the shape of .the comparativelywide connecting channel is such that due to its having suitably shapedperforated partitions, for example, there is apassage for the vapour,but the mercury cannot flow from the separate container even if thevessel is turned upside down.

Germany November 11, 1938 The above solutions have, however, thedisadvantage that, particularly in the case of shocks of the vessel, themercury can still pass through it or that there is only an extremelynarrow aperture for the passage of the mercury vapour.

The object of the invention is to insert, in the connecting channel, aseparating member which on the one hand fully avoids the discharge ofliquid mercury and on the other hand permits of altering the resistanceto the passage of vapour to accord as far as possible with practicalrequirements without the perfect fulfillment of the first-mentionedcondition being impaired even to the slightest extent.

According to the invention, use is made for this purpose of a separatingmember-having a large number of fine passages or apertures each of whichis small enough to prevent the liquid mercury from passing through theapertures under the conditions prevailing in the tube, the sum of thelatter apertures enabling equalisation of the mercury vapour, existingon both sides, to the extent required in the circumstances.

In view of the above-described difliculties during heating-up of thetube after an interval of operation it is preferable that the flowingresistance of the filter should be such that the quantity of mercuryvapour necessary for obtaining the operative vapour pressure in the tuberequires an amount of time for its passage into the discharge spacewhich exceeds that in which the tube assumes its operative temperature.Thus the premature passage of an excessive quantity of mercury vapour isavoided in the heating-up period.

The term flowing capacity as used herein and in the claims is to beunderstood to-mean the number of milligrams of mercury in its vaporizedstate which will pass through the filter in one minute with adifferential pressure of 1 mm. of Hg.

For this reason it is preferable, particularly in the case of highvoltage current converting tubes having intermediate electrodes arrangedbetween the anode and the cathode for the purpose of regulating thevoltage that the flowing resistance of the filter should be such thatduring the heating-up period of the tube the deposit of liquid mercuryon the said intermediate electrodes is avoided.

It is preferable that. the porous separating body should be sinteredtogether from a powder terial.

In order that the invention maybe clearly understood and readily carriedinto eflect it will now be described more fully with reference to theaccompanying drawing.

The single figure of the drawing shows an incandescent cathode rectifiertube having a mercury vapour filling for very high voltages up to about180 kilovolts peak voltage in the non-conducting direction. Thedischarge vessel of this tube is constituted by a glass member Icarrying the stem 2 of the helical incandescent cathpde 3 which isactivated by means of barium oxide and is provided with a screen 4. Thesaid glass part has connected to it in alternative order the wall'partsof metal 5, 6, 1, 8, 9 and I and also the wall parts of glass H, l2, l3,H, II and it, of which the latter one constitutes the lower closure ofthe vertically arranged rectifier tube. This part It is provided withacomparatively narrow cylindrical extension l1 the lower end of whichcontains a small supply of mercury l8 which, due to correctproportioning of the extension, assumes, the temperature necessary formaintaining the desired vapour pressure of about 1 to 6 microns, viz, 20to 40 C. The supply of mercury I! is separated from the discharge spaceproper by a so-called glass filter I9, that is to say, a porous memberwhich is made of glass finely pulverized and then sintered together, orin some cases of ceramic material, and which has such a cross-sectionalarea that irrespective of the conditions the passage of mercury vapourthrough the filter is practically precluded from being interfered withby the liquid mercury. Even if in themost unfavourable case the totalsupply of liquid mercury would exist on the upper surface of the filterthe equalization of the mercury vapour would nevertheless by effectedtowards below in an almost unhampered manner in view of the favourablecondi-- tions of the free filter surface and of the part of the surfacethat may be covered by mercury.

In the construction according to the invention it has been foundpossible to confine the liquid mercury under all operating conditions tothe supply container provided for it and in contradistinction to thegreater part of well-known con structions the liquid mercury isprevented from passing through the filter even in the case of mostviolent shaking.

The construction according to the invention permits of the flowingresistance of'the separating member being proportioned to the optimumextent; this results from view points which may be explained mostefiiciently with reference to a practical example:

It may occur in practice that the rectifier tube is out of use by night,it being possible for the temperature in unfavourable cases (portablesystems in open air) to assume even values of minus 10 C. In this casean increase in temperature of 25 C. is required for putting the tubeinto use at the lowest admissible temperature of C.

During the heating-up process a temperaturelag of the metal electrodesor the screens may occur since their thermal contact with the heattransmitting surfaces is often unsatisfactory and their thermal capacityis high. The temperature, for example, of the metal rings of the tube,

described is consequently temporarily lower than that of the glass sothat condensed mercury becomes deposited on the rings which in turnentails the risk of back-ignitions.

\ In this case it is necessary for the resistance of the glass filter tobe maintained at such a value that the rate of the mercury vapour flowin the direction of the discharge vessel is limited to such a value thatany excessive quantity of mercury vapour that may become deposited inthe manner described does not become available.

The factors decisive in view. thereof, that is to say the thermalcapacity of the tube parts, the thermal contact resistances on thecontacting surfaces and also the energy and arrangement of the source ofheat are so different in practice that itis impossible to give a generalrule for proportioning.v On the other hand there is, however, not theleastdifiiculty in each separate case to ascertain, by practicalexperiments, the value the flowing resistance of the filter must have toavoid condensation on the electrodes during heating-up and on the otherhand, however, to obtain the value 01' the vapour pressure necessary forthe use of the tube within a time period which may not be too long forpractice, for example 01' 15 minutes.

The requisite supply of mercury is distilled into the tube duringpumping through a suction tubule 23 and, after the tube has been scaledoi! the'pump, is distilled thence into the lower part of the extensionI! by heating the tube in a furnace. For this purpose it is necessaryfor the lower part of I! to protrude from the furnace so as to assume alower temperature.

It is advisable to avoid contamination oi the filter surface adjacentthe discharge space due, for example to electrode particles that havesprung off, by suitable screens. In the construction described thisresult is obtained due tothe fact that the metal cylinder 20 whichrepresents the main anode of the tube and is arranged within the metalwall part III also constitutes a closure of the lower part of the tubeso that this special part which surrounds the supply of mer-' cury I8and the filter I9 only communicates freely with the discharge tubeproper through lateral apertures 2|. Since the tube is used in thevertical position shown particles falling from the cathode 3 will fallon to the anode bottom 22 and cannot contaminate the filter l9.

It is an advantage of the separating body according to the inventionthat it can be arranged at any spot of the discharge vessel when thelatter is the coldest spot. of the tube and that in this case the supplyof mercury can also be arranged above the separating body without therebeing any risk that liquid mercury'may pass into the discharge space.

What I claim is: p

1. An ionic discharge tube comprising an envelope having a reservoirportion and a connecting portion connecting said reservoir portion tothe main discharge space of the tube, a sup,- ply of liquid mercury in'said reservoir portion, an anode and cathode within said envelope andspaced apart to form a discharge path, and means in said connectingportion to prevent passage of the liquid mercury to the main discharge.

space under any condition while allowing equalization of the pressure ofthe mercury vapor in said reservoir portion and the discharge space,said means comprising a porous member having a flowing capacity notgreater than that value at which the time required to obtain theoperative vapor'pressure in the tube is equal to thetime required forthe tube to reach its operating temperature. v

2. An ionic discharge tube comprising an en'- velope having a reservoirportion and a connecting portion connecting said reservoir portion toand in the discharge space, said means comprising a porous member havinga flowing capacity less than that value at which mercury deposits onsaid intermediate electrode during the heating-up of the tube.

3. An ionic discharge tube comprising an envelope having a reservoirportion and a connecting portion connecting said reservoir portion tothe main discharge space of the tube, a supply of liquid mercury in saidreservoir portion, an anode and cathode within said envelope and spacedapart to form a discharge path, and means in said connecting portion toprevent passage of the liquid mercury to the main discharge space underany condition while allowing equalization of the pressure of the mercuryvapor in said reservoir portion and the discharge space, said meanscomprising a porous member of sintered material having a flowingcapacity not greater than that value at which the time required toobtain the operative vapor pressure in the tube is equal to the timerequired for the tube to reach its operating temperature.

MARI JOHAN DRUYVESTEYN/

